An adaptive threshold setting method and system for photomultiplier tube signals used in ultraviolet communication

Abstract

This invention discloses an adaptive threshold setting method and system for photomultiplier tube (PMT) signals used in ultraviolet (UV) communication. The method involves setting an initial threshold, a threshold variation step size, and the number of parallel thresholds for the PMT. Centered on the initial threshold, a set of n different thresholds is generated using the threshold variation step size. For each signal received by the PMT, multiple decision results are generated based on the different thresholds in the set. Performance indicators of each decision result are calculated and compared to evaluate the merits of different thresholds in the resulting set. The selected optimal threshold is updated as the current working threshold. The signal data received by the PMT is continuously monitored and processed, and the above operations are repeated to dynamically adjust the current threshold. This method solves the problems of inflexible threshold setting, high resource consumption, and slow response speed in variable communication scenarios, thereby achieving accurate detection and real-time processing of PMT signals.

Description

Technical Field

[0001] This invention relates to the field of signal processing technology in wireless optical communication, and in particular to an adaptive threshold setting method and system for photomultiplier tube (PMT) signals used in ultraviolet communication. Background Technology

[0002] After the photomultiplier tube (PMT) acquires the signal, the signal is input to the analog-to-digital converter (ADC). During photon counting, the PMT detects not only photons from the target signal but also background noise photons. To extract the valid signal, a threshold needs to be set, with signals below this threshold considered noise and signals above it considered valid. Common threshold setting methods include empirical methods based on experimental data and statistical methods that analyze the statistical distribution of noise and signal to select a threshold that can effectively distinguish between noise and signal.

[0003] In practical communication scenarios, setting the optimal threshold for a PMT presents several challenges. First, signal strength and noise levels may dynamically change under different environments, and a fixed threshold may not be effective after drastic changes in environmental conditions. Second, the threshold setting also needs to consider the thermal noise level and sensitivity characteristics of different PMTs themselves.

[0004] Existing adaptive algorithms, including mean-variance adaptive algorithms based on statistical characteristics, Kalman filters and other adaptive filter algorithms, as well as machine learning algorithms, have achieved significant results in widespread applications. However, these algorithms also face their own challenges in threshold adaptation of PMT signals. Mean-variance adaptive thresholding methods rely on the calculation of statistical characteristics and are not quick enough to adjust under drastic environmental changes; adaptive filter algorithms may require complex matrix operations and filtering operations, which consume a large amount of storage resources on FPGAs, limiting their application in resource-constrained environments; machine learning algorithms are typically computationally complex and require a large amount of memory and computing power, making them unsuitable for rapidly changing environments and significantly increasing resource consumption. Therefore, in dynamic communication scenarios, there is a need to develop an algorithm that can adapt quickly and consumes fewer resources. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for adaptive threshold setting of photomultiplier tube signals for ultraviolet communication. This method and system can solve the problems of inflexible threshold setting, large resource consumption, and slow response speed in variable communication scenarios, thereby achieving accurate detection and real-time processing of PMT signals.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] An adaptive threshold setting method for photomultiplier tube signals used in ultraviolet communication, the method comprising:

[0008] Step 1: Set the initial threshold, threshold change step size, and number of parallel thresholds for the photomultiplier tube;

[0009] Step 2: Using the set initial threshold as the center, generate a set of n different thresholds by using the threshold change step size. This set is used for different decision conditions in subsequent signal processing.

[0010] Step 3: For each signal received by the photomultiplier tube, generate multiple sets of decision results based on different thresholds in the set obtained in Step 2. The decision results are the detection results of the signal or the conditions required for calculating other performance evaluations.

[0011] Step 4: Calculate and compare the performance indicators of each set of decision results based on the generated multiple sets of decision results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the merits of different thresholds in the obtained set through performance indicators;

[0012] Step 5: Based on the evaluation results of Step 4, select the threshold that optimizes system performance and update the selected threshold to the current working threshold.

[0013] Step 6: Continuously monitor and process the signal data received by the photomultiplier tube, repeat the operations of steps 2-5, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

[0014] An adaptive threshold setting system for photomultiplier tube signals used in ultraviolet communication, the system comprising:

[0015] The parameter initialization module is used to set the initial threshold, threshold change step size, and number of parallel thresholds for the photomultiplier tube.

[0016] The threshold set generation module is used to generate a set of n different thresholds centered on the set initial threshold and using the threshold change step size. This set is used for different decision conditions in subsequent signal processing.

[0017] The signal receiving and processing module is used to generate multiple sets of decision results for each signal received by the photomultiplier tube based on different thresholds in the obtained set. The decision results are either the detection results of the signal or the conditions required to calculate other performance evaluations.

[0018] The performance evaluation module is used to calculate and compare the performance indicators of each set of decision results based on the generated multiple sets of decision results, including bit error rate, signal strength and signal-to-noise ratio, and to evaluate the merits of different thresholds in the obtained set through performance indicators;

[0019] The optimal threshold selection module is used to select the threshold that optimizes system performance based on the evaluation results, and update the selected threshold to the current working threshold.

[0020] The dynamic adjustment and feedback module is used to continuously monitor and process the signal data received by the photomultiplier tube, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

[0021] As can be seen from the technical solutions provided by the present invention, the above methods and systems can solve the problems of inflexible threshold setting, large resource consumption, and slow response speed in variable communication scenarios, thereby achieving accurate detection and real-time processing of PMT signals. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of a photomultiplier tube signal adaptive threshold setting method for ultraviolet communication provided in an embodiment of the present invention;

[0024] Figure 2 The outdoor experiment exemplified by this invention illustrates different threshold conditions for λ. s and λ b A schematic diagram illustrating the changing trends;

[0025] Figure 3 This is a schematic diagram of the system described in an embodiment of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, and do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0027] like Figure 1 The diagram shows a flowchart of a photomultiplier tube signal adaptive threshold setting method for ultraviolet communication provided by an embodiment of the present invention. The method includes:

[0028] Step 1: Set the initial threshold, threshold change step size, and number of parallel thresholds for the photomultiplier tube;

[0029] In this step, the initial threshold V is specifically set. th Threshold change step size ΔV th And the number of parallel thresholds, n;

[0030] Wherein, the initial threshold V th and threshold change step size ΔV th All values ​​are quantized digital signals acquired by analog-to-digital converters (ADCs), where n is an odd number not less than 3.

[0031] Threshold change step size ΔV th The values ​​of and n are set according to the response speed requirements of the adaptive algorithm and the limitations of system resources to ensure the efficiency and accuracy of the adaptive process.

[0032] Step 2: Using the set initial threshold as the center, generate a set of n different thresholds by using the threshold change step size. This set is used for different decision conditions in subsequent signal processing.

[0033] In this step, the initial threshold V is calculated. th Centered on the threshold, the step size ΔV is used to calculate the threshold variation. th Generate a set containing n different thresholds. Represented as:

[0034]

[0035] Where k is the index, indicating from arrive Integer value.

[0036] Step 3: For each signal received by the photomultiplier tube, generate multiple sets of decision results based on different thresholds in the set obtained in Step 2. The decision results are the detection results of the signal or the conditions required for calculating other performance evaluations.

[0037] In this step, during the communication process, the optical signal received by the photomultiplier tube (PMT) is input to the analog-to-digital converter (ADC), which converts the analog signal into a digital signal.

[0038] For the digital signal acquired by the ADC, n different thresholds in the set T obtained in step 2 are used to make a decision and generate n decision results.

[0039] The above n decision result sequences are processed for frame synchronization using a synchronization header. Based on the decision result sequence for each threshold, the photon count rate λ of the received optical signal is calculated respectively. s and background noise photon count rate λ b .

[0040] In practical applications, the calculated λs With λ b Rounding can be performed according to the actual limitations of the platform.

[0041] Step 4: Calculate and compare the performance indicators of each set of decision results based on the generated multiple sets of decision results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the merits of different thresholds in the obtained set through performance indicators;

[0042] In this step, n different λ values ​​are obtained. s With λ b Next, the bit error rate (BER) is calculated separately as a reference for comparing the merits of the n threshold groups in the comparison set. Specifically:

[0043] Based on the log-likelihood ratio L(N) used in the decision, it is expressed as:

[0044]

[0045] Where N represents the number of photon pulses within a symbol; assuming the noise and signal have the same N value, i.e., N... b and N s Each independently satisfies λ b With λ s The Poisson distribution, N b and N s Let represent the number of photon pulses from the optical signal and the number of photon pulses from the background noise within a symbol, respectively. Then, the probability of misclassifying 0 as 1 is expressed as:

[0046]

[0047] P() represents N b The probability of satisfying the conditions in parentheses is the same below;

[0048] The probability of misclassifying 1 as 0 is expressed as:

[0049]

[0050] The calculated bit error rate (BER) is expressed as:

[0051]

[0052] In the actual implementation, the number of 0s and 1s in the frame synchronization header is designed to be close to 1:1.

[0053] Step 5: Based on the evaluation results of Step 4, select the threshold that optimizes system performance and update the selected threshold to the current working threshold.

[0054] In this step, based on the evaluation results of step 4, the threshold corresponding to the group with the lowest bit error rate (BER) is set as the current optimal threshold. The index corresponding to the group with the lowest BER is represented as follows:

[0055] i opt =arg min i BER i

[0056] Where the subscript i represents the bit error rate (BER) corresponding to the i-th threshold; argmin represents finding the index i that minimizes the BER. opt ;

[0057] The optimal threshold is V th +i opt ·ΔV th Assign the optimal threshold to the initial threshold V. th Update to the current working threshold.

[0058] Step 6: Continuously monitor and process the signal data received by the photomultiplier tube, repeat the operations of steps 2-5, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

[0059] In the specific implementation, to further conserve platform resources when calculating the bit error rate (BER), this embodiment adopts a method of importing a relative BER sorting table into the ROM. This sorting table pre-calculates and stores different λ values. b With λ s The relative magnitudes of the bit error rate (BER) under the combined values ​​are used by the system to quickly compare the results under various thresholds through a table lookup method during actual operation, thereby reducing the burden of real-time computation. Part of the structure of this sorting table is shown in Appendix 1:

[0060] Appendix 1: Partial Example of BER Relative Size Sort Table

[0061]

[0062] The actual table may contain more combinations and corresponding relative bit error rates (BER).

[0063] Based on the above method embodiments, the present invention also provides a photomultiplier tube signal adaptive threshold setting system for ultraviolet communication, such as... Figure 3 The diagram shown is a structural schematic of the system according to an embodiment of the present invention. The system includes:

[0064] The parameter initialization module is used to set the initial threshold, threshold change step size, and number of parallel thresholds for the photomultiplier tube.

[0065] The threshold set generation module is used to generate a set of n different thresholds centered on the set initial threshold and using the threshold change step size. This set is used for different decision conditions in subsequent signal processing.

[0066] The signal receiving and processing module is used to generate multiple sets of decision results for each signal received by the photomultiplier tube based on different thresholds in the obtained set. The decision results are either the detection results of the signal or the conditions required to calculate other performance evaluations.

[0067] The performance evaluation module is used to calculate and compare the performance indicators of each set of decision results based on the generated multiple sets of decision results, including bit error rate, signal strength and signal-to-noise ratio, and to evaluate the merits of different thresholds in the obtained set through performance indicators;

[0068] The optimal threshold selection module is used to select the threshold that optimizes system performance based on the evaluation results, and update the selected threshold to the current working threshold.

[0069] The dynamic adjustment and feedback module is used to continuously monitor and process the signal data received by the photomultiplier tube, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

[0070] The specific implementation methods of each module in the above system are described in the above method embodiments.

[0071] In practice, the general framework of this adaptive threshold setting system can be extended to various adaptive systems in other fields, such as adaptive control and adaptive data processing systems. Each module can be customized according to the specific application requirements to adapt to different working conditions and performance requirements.

[0072] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0073] The method described in this embodiment of the invention is illustrated below with a specific example. In this example, the experimental system uses an ultraviolet LED as the transmitter and a PMT as the receiver. The experiment is conducted outdoors on a sunny day, with a distance of approximately 50 meters between the transmitter and receiver. Each chip in the system contains 80 sampling points, and each symbol consists of 10 chips. The specific steps include:

[0074] Step 1: Set the initial threshold V th =30, threshold change step size ΔV th =3, the number of parallel thresholds n=3, that is, 3 sets of thresholds in parallel. ΔV th The values ​​of and n are set according to the response speed requirements of the adaptive algorithm and the limitations of system resources.

[0075] Step 2: Calculate V th Centered on the threshold, the threshold change step size is ΔV th The threshold set, which contains 3 values, is represented as follows: That is, set

[0076] Step 3: During communication, the optical signal received by the photomultiplier tube (PMT) is input to the analog-to-digital converter (ADC) to convert the analog signal into a digital signal; for the digital signal acquired by the ADC, a set of... Three different thresholds are used to make decisions.

[0077] The synchronization header is used to perform frame synchronization processing on the above three decision result sequences. Based on each threshold decision result sequence, the photon count rate λ of the received optical signal is calculated. s and background noise photon count rate λ b The calculated λ s With λ b Rounding is performed due to platform limitations.

[0078] Step 4: Obtain 3 different sets of λ s and λ b Next, the theoretical bit error rate (BER) was estimated as a reference for comparing the merits of the three threshold groups. Specifically:

[0079] Based on the log-likelihood ratio L(N) used in the decision, assume the values ​​of N for noise and signal, i.e., N b and N s Each independently satisfies λ b With λ s If the distribution follows a Poisson distribution, the probability of misclassifying 0 as 1 is:

[0080]

[0081] The probability of misclassifying 1 as 0 is:

[0082]

[0083] The estimated bit error rate

[0084] Step 5: For each decision result, based on the calculated channel parameter λ... s With λ b Estimate the bit error rate (BER) of each group and set the threshold corresponding to the group with the lowest BER as the current optimal threshold.

[0085] The index corresponding to the group with the lowest bit error rate is i. opt =arg min i BERi ;

[0086] The optimal threshold is V th +i opt ·ΔV th Assign the optimal threshold to the initial threshold V. th Update to the current working threshold.

[0087] Step Six: Continuously monitor and process the received signal data in real time, repeating steps two through five, and dynamically adjust the threshold to ensure that the system maintains optimal detection performance under various environmental conditions.

[0088] During the experiment, λ was recorded under different threshold conditions. s and λ b The changing trend was shown, and a trend chart was drawn, such as... Figure 2 The figure shows λ under different threshold conditions in an outdoor experiment, as exemplified by the present invention. s and λ b A diagram illustrating the changing trends, from Figure 2 As can be seen from this, the initial threshold V set when the system starts up th =30 is not effective, so λ s Ratio λ b Small. After approximately 10 frames of transmission, the threshold adaptively reached λ. s Ratio λ b Large position.

[0089] Around frame 80, the experimenters used an umbrella to shield the receiver PMT from sunlight, but did not block the light path emitted by the ultraviolet LED to the PMT. λ can be observed. b A sudden drop occurred, and at the same time λ s The value increases sharply, and after threshold adaptation, λ s It has been increased to a higher value.

[0090] Around frame 270, the experimenters retracted the umbrella that was blocking the sunlight, causing λ to... s A sharp drop, while λ b It rises sharply. After a period of time, the threshold is adaptively adjusted again, making λ... s Restored to a value greater than λ b Large position.

[0091] The above experimental results show that the method described in the embodiments of the present invention can effectively cope with changes in ambient light intensity, ensure that the optimal threshold setting can be maintained under different environmental conditions, and improve the reliability and performance of the ultraviolet communication system.

[0092] In summary, the method described in the embodiments of the present invention has the following advantages:

[0093] 1. The method proposed in this invention can significantly improve the accuracy of signal detection by dynamically adjusting the threshold, compared with a fixed threshold, thereby improving the overall performance and reliability of the communication system;

[0094] 2. The method proposed in this invention can respond in real time to changes in environmental conditions, such as light intensity and meteorological factors, ensuring that the optimal threshold setting can be maintained under different environments, thereby improving communication quality.

[0095] 3. Compared with existing adaptive algorithms, the method proposed in this invention can reduce the system's demand for storage and computing resources, optimize the use of hardware resources, and improve the overall efficiency of the system.

[0096] Furthermore, those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware, and the corresponding program can be stored in a computer-readable storage medium, such as a read-only memory, a disk, or an optical disk.

[0097] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for adaptive threshold setting of photomultiplier tube signals for ultraviolet communication, characterized in that, The method includes: Step 1: Set the initial threshold, threshold change step size, and number of parallel thresholds for the photomultiplier tube; Step 2: Using the set initial threshold as the center, generate a set of n different thresholds by using the threshold change step size. This set is used for different decision conditions in subsequent signal processing. Step 3: For each signal received by the photomultiplier tube, generate multiple sets of decision results based on different thresholds in the set obtained in Step 2. The decision results are the detection results of the signal. Step 4: Calculate and compare the performance indicators of each set of decision results based on the generated multiple sets of decision results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the merits of different thresholds in the obtained set through performance indicators; Step 5: Based on the evaluation results of Step 4, select the threshold that optimizes system performance and update the selected threshold to the current working threshold. Step 6: Continuously monitor and process the signal data received by the photomultiplier tube, repeat the operations of steps 2-5, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

2. The adaptive threshold setting method for photomultiplier tube signals for ultraviolet communication according to claim 1, characterized in that, In step 1, an initial threshold is set. Threshold change step size And the number of parallel thresholds, n; Among them, the initial threshold and threshold change step size All values ​​are quantized digital signals acquired by analog-to-digital converters (ADCs), where n is an odd number not less than 3. Threshold change step size The values ​​of and n are set according to the response speed requirements of the adaptive algorithm and the limitations of system resources.

3. The adaptive threshold setting method for photomultiplier tube signals for ultraviolet communication according to claim 1, characterized in that, The process of step 2 is as follows: Calculated using the initial threshold Centered on the threshold, the step size of the threshold change is used. Generate a set containing n different thresholds. , represented as: Where k is the index, indicating from arrive Integer value.

4. The adaptive threshold setting method for photomultiplier tube signals for ultraviolet communication according to claim 3, characterized in that, In step 3, during the communication process, the optical signal received by the photomultiplier tube (PMT) is input to the analog-to-digital converter (ADC), which converts the analog signal into a digital signal. For the digital signals acquired by the ADC, the set obtained in step 2 Given n different thresholds, make judgments for each and generate n judgment results; The synchronization header is used to perform frame synchronization processing on the above n decision results. Based on the decision result of each threshold, the photon count rate of the received optical signal is calculated respectively. and background noise photon count rate .

5. The photomultiplier tube signal adaptive threshold setting method for ultraviolet communication according to claim 4, characterized in that, The process of step 4 is as follows: After obtaining n different sets and Next, the bit error rate (BER) is calculated separately as a reference for comparing the merits of the n threshold groups in the comparison set. Specifically: Based on the log-likelihood ratio used in the decision , is represented as: Where N represents the number of photon pulses within a symbol; assuming the values ​​of N for noise and signal, i.e. and Each independently satisfies and The Poisson distribution, and Let represent the number of photon pulses from the optical signal and the number of photon pulses from the background noise within a symbol, respectively. Then, the probability of misclassifying 0 as 1 is expressed as: P() represents The probability of satisfying the conditions within the parentheses; The probability of misclassifying 1 as 0 is expressed as: The calculated bit error rate (BER) is expressed as: 。 6. The adaptive threshold setting method for photomultiplier tube signals for ultraviolet communication according to claim 5, characterized in that, In step 5, based on the evaluation results of step 4, the threshold corresponding to the group with the lowest bit error rate (BER) is set as the current optimal threshold. The index corresponding to the group with the lowest BER is represented as follows: in This represents the bit error rate (BER) corresponding to the i-th threshold. This indicates the search for the index that minimizes the bit error rate (BER). ; The optimal threshold is Assign the optimal threshold to the initial threshold. Update to the current working threshold.

7. A photomultiplier tube signal adaptive threshold setting system for ultraviolet communication, characterized in that, The system includes: The parameter initialization module is used to set the initial threshold, threshold change step size, and number of parallel thresholds for the photomultiplier tube. The threshold set generation module is used to generate a set of n different thresholds centered on the set initial threshold and using the threshold change step size. This set is used for different decision conditions in subsequent signal processing. The signal receiving and processing module is used to generate multiple sets of decision results for each signal received by the photomultiplier tube based on different thresholds in the obtained set. The decision results are the detection results of the signal. The performance evaluation module is used to calculate and compare the performance indicators of each set of decision results based on the generated multiple sets of decision results, including bit error rate, signal strength and signal-to-noise ratio, and to evaluate the merits of different thresholds in the obtained set through performance indicators; The optimal threshold selection module is used to select the threshold that optimizes system performance based on the evaluation results, and update the selected threshold to the current working threshold. The dynamic adjustment and feedback module is used to continuously monitor and process the signal data received by the photomultiplier tube, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

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